Hitherto, a reaction tube which is used to synthesize a carbon nanotube by a fluid bed process is formed in a tube shape extending straightly. Then, a distributor provided with penetration holes is disposed inside the reaction tube, and a heating device is disposed outside the reaction tube. When a carbon nanotube is synthesized by using such a reaction tube, a granular carrying medium that carries catalytic particles is first charged in the reaction tube so that the granular carrying medium is held by the distributor. Next, a feed gas is supplied from the lower side of the reaction tube while the reaction tube is heated by the heating device, and the granular carrying medium is fluidized by the feed gas. Accordingly, the feed gas is circulated on the granular carrying medium, and the carbon nanotube is grown from carbon nanotube synthesis catalysts carried by the granular carrying medium.